In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drive trains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drive train, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost.
The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drive train in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at reduced levels compared to conventional vehicles. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drive train of a hybrid vehicle is typically much more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, or multiple electric motors, thereby eliminating one source of pollution while significantly reducing drive train complexity.
The electric drive trains used in electric vehicles have proven to be highly reliable and capable of providing exceptional performance. Unfortunately car sales for electric vehicles have proven to be lower than one would expect, especially given the performance and reliability of these cars. It appears that these sluggish sales are due, at least in part, to the concerns of many potential buyers regarding the limited driving range when an electric vehicle is new, and the loss of driving range as the car ages. These concerns may be further exacerbated by the relatively complex relationships between battery lifetime and charge rate (illustrated in FIG. 1) and between battery lifetime and the level of charge maintained during storage (illustrated in FIG. 2), relationships that a typical car owner/buyer may have heard of but typically will not fully understand. As a result of not fully understanding the effect that charge rate and state-of-charge (SOC) have on battery life, even if a vehicle permits the driver to set charging parameters, a typical car owner finds it difficult to optimize these parameters. Accordingly, what is needed is a system that provides the user with a relatively constant driving range for a given vehicle lifetime, thus eliminating the fears associated with range loss as the car ages, and one which does not require the user to set and/or monitor charging parameters in order to maintain this driving range. The present invention provides such a system.